Recently, in displays, conventional cathode ray tubes (CRTS) have been converted into flat panel displays, such a plasma display panel (PDP), a liquid crystal display (LCD), an organic light emitting diode (OLED) and the like. Particularly, in order to realize such flat panel displays into flexible displays in the future, research thereinto is going on all over the world.
In such a flat panel display, basically, a substrate is made of a glass material. Meanwhile, in a general flat panel display, high-temperature heat treatment is required to form a thin film transistor (TFT), and thus a glass substrate has been used as the most suitable substrate therefore.
However, the glass substrate is problematic in that it is not suitable as a substrate for flexible displays because it is excessively rigid, that is to say, its flexibility is poor.
Therefore, research into technologies of manufacturing a substrate for flexible displays using a plastic material, wherein the substrate for flexible displays is superior to a glass substrate in terms of formability, durability, design and the like, and particularly, can be produced through a roll to roll method so as to reduce the production cost thereof, has actively been conducted. However, such a substrate for flexible displays, made of a plastic material, has not been developed yet to such a degree that it is commercially available.
Meanwhile, touch screen panels (TSPs) are used in flat panel displays, such as electronic notepads, liquid crystal displays (LCDs), plasma display panels (PDPs), electroluminescent panels, and cathode ray tubes (CRTs), and are intended to allow a user to select desired information through such displays. Touch screen panels (TSPs) are largely classified into resistive type touch screen panels, capacitive type touch screen panels and resistive-multi-touch type touch screen panels.
Such a resistive type touch screen panel is made by applying a resistive material onto a glass or plastic substrate and then covering the substrate with a polyethylene film, and is configured such that insulation rods are provided at regular intervals to prevent the two faces from coming into contact with each other. The operating principle thereof is as follows. When predetermined electric current is applied to both ends of a resistive film, the resistive film acts as a resistor, and thus voltage is generated between both ends thereof. When a user's finger comes into contact with the resistive type touch screen panel, the polyester film formed on the upper surface of the substrate warps, and thus the two faces are connected to each other. Therefore, owing to the resistive components of the two faces, the two faces are disposed in the form of a parallel connection of resistors, and the change in a resistance value occurs. In this case, voltage is changed by electric current flowing through both ends of the resistive film, and the position of the finger making contact with this touch screen panel can be recognized by the degree of change in voltage. This resistive type touch screen panel is advantageous in that it has high resolution and rapid response speed because it is operated by surface pressure, but is disadvantageous in that it can activate only one point and is in danger of being damaged.
Further, such a capacitive type touch screen panel is made by applying a special conductive metal to both sides of heat-treated glass. When voltage is applied to the four edges of the touch screen panel, high frequency waves spread to the entire surface of a sensor. At this time, when a user's finger comes into contact with this touch screen panel, the flow of electrons is changed, and such a change is detected, thus recognizing coordinates. This capacitive type touch screen panel is advantageous in that it can be activated by simultaneously pushing several points and has high resolution and excellent durability, but is disadvantageous in that it has a low response speed and is difficult to mount.
Finally, such a resistive-multi-touch type touch screen panel is realized such that it can be activated in the same manner as in the capacitive type touch screen panel by making up for the worst disadvantage of the resistive type touch screen panel capable of activating only one point.
Meanwhile, touch screen panels (TSPs) are selected for individual electronic products in consideration of their respective characteristics, such as optical characteristics, electrical characteristics, mechanical characteristics, environment-resistant characteristics, input characteristics, durability and economical efficiency, as well as signal amplification problems, resolution differences and degree of difficulty in a processing technology. Particularly, resistive type and capacitive type touch screen panels are widely used in electronic notepads, personal digital assistants (PDAs), portable PCs, mobile phones and the like.
In the technology of manufacturing a touch screen, in the future, it will required to reduce the thickness of a touch screen panel in order for the touch screen panel to have sufficient durability while simplifying complicated processes as much as possible. The reason for this is that, even when the brightness of a display is lowered by increasing light transmittance, the same performance as that of the existing product is realized, and thus power consumption can be reduced, thereby increasing the life time of a battery.
There has been proposed a general resistive type touch screen panel.
Explaining the general resistive type touch screen panel, this resistive type touch screen panel includes: a window film (or overlay film) provided on one side of a liquid crystal display device; and first/second ITO films attached to the lower surface of the window film and provided to electrically input information to a liquid crystal display module, wherein the window film is provided to protect the first ITO film. The window film (or overly film) is generally made of polyethylene terephthalate (PET), and the first ITO film is attached to the window film (or overly film) by an optical clear adhesive (OCA). The first and second ITO films are printed on the edges thereof with first and second electrode layers made of silver, respectively. Here, a double-sided tape for insulation is provided between the first and second electrode layers, and the first and second electrode layers are spaced from each other at a predetermined interval by a dot spacer, so these first and second electrode layers are electrically connected with each other when external pressure (touch) is applied by a finger or a touch pen, thereby detecting an accurate touch position.
In this case, this resistive type touch screen panel is problematic in that its light transmittance is deteriorated due to a lamination process of attaching the first ITO film to the window film (or overlay film) using an optical clear adhesive (OCA), and in that processing treatment becomes complicated and processing cost increases because a process of disposing the window film (or overlay film) and a process of attaching the first ITO film to the window film (or overlay film) using the optical clear adhesive (OCA) must be separately carried out.
Further, this resistive type touch screen panel is problematic in that ITO cannot be selectively applied onto the desired region of the window film (or PET film) because the ITO film is patterned by wet etching using laser.
Generally, in the manufacture of a touch screen, a polyethylene terephthalate (PET) film is used as a transparent substrate. However, the PET film is advantageous in terms of a cost, but is disadvantageous in that it has low heat resistance to such a degree that it is deformed at 130° C. or higher.
Therefore, when a subsequent heat treatment process is carried out with a PET film deposited with an indium tin oxide (ITO) film, the PET film is expanded or contracted, thus causing the ITO film to become loose or to be cracked. In order to prevent such an undesirable phenomenon, a method of carrying out a subsequent process after a primary process of previously exposing a transparent substrate to high temperature for a long period has recently been used.
However, this method is also problematic in that such a pretreatment process serves to increase the time taken to manufacture a touch screen, thus decreasing the production rate thereof.